(a). Field of the Invention
This invention relates to a communication system, and more particularly, to an apparatus and method for automatic gain control for the communication system.
(b). Description of the Prior Arts
In general, a receiver in the communication field needs to fix a received signal at a specific power level. Such mechanism is called automatic gain control (AGC). In prior art, a receiver first detects the signal power received and compares it with a threshold level to generate a comparison signal, and then feeds the comparison signal back to a front-end programmable-gain amplifier (PGA) or a variable-gain amplifier (VGA) to adjust the received signal power. In this manner, the receiver, within a reasonable received power range, can lock the received signal power at a desired level.
However, since the prior art determines how to adjust the signal power according to the comparison of total power of the received signal with the threshold level, the received power level will be deviated when the received signal is mixed with undesired interference. Thus, more quantization noise might be generated during the analog-to-digital signal conversion to degrade the receiver performance.
Other conventional technologies use an additional interference detector to reduce the interference effect. However, the additional circuit means a higher cost, and the interference detector might not work if there is undetectable interference.